.Net 4.5 is backword compatible with 4, but 4.5 has additional classes that the newer Kenticos may employ. It shouldn't be hard to do this though, usually the .net DLLs are in the LIB folder that you can pull from. If the instructions don't say how to get the 4.5 drivers, install a 4.5 instance of kentico, and grab the LIB folder (may be able to find it in the installation folder as well to save time).